The invention relates to a method for the production of porous fiber bats of coiled or loose fibers put into the form of a felt- or wadding-like structure, in which they are brought into contact with an agent for joining the fibers together.
The German unexamined specification No. 2,750,960 describes the use of bats as filters for diesel exhaust gas. The fiber felt consisting of loose fibers is for this purpose surrounded with support members and on the downstream side is additionally provided with woven fiber pads in order to prevent the gas flow from dislodging the loose fibers. However it is still not possible to prevent some of the fibers being entrained by the current of gas and being deposited on the upstream side of the woven pad and even becoming lodged in its pores.
However it has been shown that fiber bats have valuable properties, more especially for filtration, since it is possible for over 90% of the suspended particles to be retained thereby, but on the other hand the working life of the material and the permanence of the porosity have been found not to be satisfactory.
Therefore attempts have been made to take suitable steps to integrate the fibers in a durable and strong structure.
The U.S. Pat. No. 3,826,076 describes a method of the initially mentioned type in which the fibers are compacted and bonded together with a silicate binder. The latter however leads to the formation of lumps and dislodges some of the fibers. The outcome is then that the fibers adhere together along a certain length thereof and the pore size is not uniform from one production batch to the next. This is illustrated in FIG. 3 of the accompanying drawings.
Another attempt at stabilizing the fibers is involved in the method of the German unexamined specification No. 2,155,507 in which bats of agglomerated fiber elements are produced which have a periphery provided with minute whiskers and form numerous interstices between them. In this case the compaction of the fiber cushion is intended not to lead to dense packing or clogging of the interstices. The particle storage capacity is considerably diminished however in this proposal owing to the agglomeration.
Fiber bats made of coiled endless fibers also involve a danger of impairment of the porosity owing to slipping of the relatively loosely coiled fibers.